The Application Of Electron Backscatter Diffraction To The Study Of Special Boundaries In Polycrystalline And Nanocrystalline Nickel Farghalli A. Mohamed, University of California, Irvine, DMR Introduction. Like a house consisting of rooms separated by walls, a polycrystalline material consists of grains separated by grain boundaries. As the number of rooms in a house increases, the number of walls required to divide them also increases and the size of each room can go down. The same is true for a polycrystalline metal: when the number of grains is increased, more grain boundaries are formed between grains and the size of each grain goes down. A metal that has very small grains is called a “nanocrystalline” material. The grain size of nanocrystalline (nc) materials is given in terms of nanometers. One nanometer is meter. The grain size of nc-materials is less than 200 nm. The orientations of rooms with respect to each other can make the house attractive in terms of appearance and value. The same is true for a “polycrystalline” material: the orientations of grains with respect to each other in a “polycrystalline” material can make the metal attractive in terms of properties such as strength. For example, grains in a polycrystalline material can be oriented in such way that boundaries exhibit a specific orientation that results in strengthening the material. These boundaries are special boundaries that are referred to as “Σ” or “coincidence site lattice (CSL)” boundaries. Results. Electron backscatter diffraction (EBSD), a technique associated with scanning electron microscopy (SEM), allows us to “map” the orientation of grains within a crystalline material and to determine the percentage of CSL boundaries within the material, in addition to other characteristics of the material’s structure. When orientation maps of large-grained polycrystalline Ni (Figure 1) and nc-Ni (Figure 2) were compared, it was found that nc-Ni possessed a greater percentage of CSL boundaries (55.2%) than large-grained polycrystalline Ni (37.3%) (Figure 3). Significance. This research is significant since it shows that the percentage of CSL boundaries in nc-Ni is much higher than that of CSL boundaries in large-grained polycrystalline Ni. This result has far reaching implications in terms of explaining the properties of nanostructured materials and their differences from those characterizing large-grained polycrystalline materials. For example, this difference was used to explain why nc-Ni has a higher corrosion resistance than that of polycrystalline Ni [1]. 50 µm0.5 µm Figure 1. Orientation map for large-grained polycrystalline Ni. (Average grain size of 40 µm.) CSL boundaries were identified and their frequency determined. Figure 2. Orientation map for nanocrystalline Ni. (Average grain size of 100 nm.) CSL boundaries were identified and their frequency determined. Figure 3. Percentage of CSL boundaries in nc-Ni and polycrystalline Ni CSL Boundaries 55.2% 37.3% References. 1. I. Roy et al., “Possible origin of superior corrosion resistance for electrodeposited nanocrystalline Ni.” Scripta Mater. 59: (2008)

FAM’s research group consists of 4 graduate students, including two female students: Heather Yang and Shehreen Dheda. Over the course of the current year, at least 30 undergraduate students have participated in research in the lab, at least 10 of which are from underrepresented minorities and/or are female: Andrew Marquez, Ricardo Komai, Joseph Yanez, Frank Jimenez, Ignacio Lopez, Chinedu Ezebuiroh, Sapphire Lopez, Karina Reyes, Ankita Bordoloi, Courtney McConnell, and Clara Druzgalski. All students, graduate and undergraduate are encouraged to participate in the Materials Outreach group at UCI. The outreach groups perform materials demonstrations for high school and community college students, typically in schools with large attendance of underrepresented minorities, in order to motivate them to pursue education and careers in science and engineering fields. Tours of laboratory facilities at UCI are given as part of the outreach efforts. The visiting students interact with our graduate and undergraduate students and are given the opportunity to ask questions about their college experiences and their future goals. Graduate and undergraduate students have also presented their research works at the TMS 2009 Annual Conference and Exhibition, SCSMM 2009 Spring Meeting, ASM Student Night for the LA Chapter 2009, and at the UCI Undergraduate Research and Opportunities Program annual spring symposium. Collaborative work has also been conducted with Boeing For the work presented in this slide, those students who have worked on this project have developed skills to use the SEM and perform EBSD. These students have gone on to use these skills in other projects in the lab as well as to participate in assisting and training students and researchers from other schools as well as from industry to conduct research using SEM and EBSD. THE APPLICATION OF ELECTRON BACKSCATTER DIFFRACTION TO THE STUDY OF SPECIAL BOUNDARIES IN POLYCRYSTALLINE AND NANOCRYSTALLINE NICKEL Farghalli A. Mohamed, University of California, Irvine, DMR